Conventionally, various diagnostic functions concerning communication are proposed in a communication system including the RFID reader/writer and the RF tag. For example, Unexamined Japanese Patent Publication No. 2010-79616 discloses a reader/writer in which a “switch” is provided such that communication can be conducted with an inspecting RF tag chip incorporated in the reader/writer. The reader/writer can conduct communication with the inspecting RF tag chip to diagnose whether a reader/writer body is normal in advance of the communication with the RF tag.
In Unexamined Japanese Patent Publication No. 2006-148670, an RF tag chip has a function of measuring radio wave intensity transmitted from the reader/writer and sending back a measured radio wave intensity to the reader/writer. Therefore, it can be known how much power transmitted from the reader/writer reaches the RF tag.
In Unexamined Japanese Patent Publication No. 2005-322029, a CPU diagnoses whether a RF tag reader/writer device or a state of the wireless communication with the RF tag is abnormal. In Unexamined Japanese Patent Publication No. 2011-138373, operating power of a “reference tag” that is incorporated in or installed outside a reader/writer antenna is measured. Reader/writer transmission power is changed in a stepwise manner during the measurement, and reader/writer minimum output power at which a normal response is sent back from the reference tag is stored.